This document specifies guidelines for the assignment of central office (CO) codes. Examples of uses for CO codes (NXX) for which these guidelines apply include plain old telephone service (POTS), Centrex, Direct Inward Dialing (DID), cellular mobile service, pagers, data lines, facsimile, coin phones, and customer owned pay phones. While these guidelines were developed at the direction of the FCC, they do not supersede controlling appropriate NANP Area governmental or regulatory principles, procedures and requirements.